Boy, it sure looks like Dax Shepard is doing all his own crazy, gonzo stunt-driving in “Hit and Run,” the car-chase comedy he wrote and co-directed.

“All me, 100 percent,” he says.

You know how you can tell? Look in the eyes of his co-star and off-camera fiancée, Kristen Bell. Yeah, she’s in the car with him in those scenes. And no, she wasn’t scared.

“Dax has always been into off-roading, so I’ve logged many hours with him in the car doing crazy tricks,” Bell says. “I know how capable he is behind the wheel, but I’m so used to it by now it doesn’t even faze me.”

Shepard is a genuine Hollywood gear head, a guy who loves his ’67 two-door, suicide-doors Lincoln so much he co-stars in the movie with it, a racer of motorcycles and dune buggies (yeah, he uses his own Baja racer in the movie, too).

“I’ve had this car thing since birth,” the Michigan native says. “My dad sold cars, and he was into dirt bikes. He raced Chevelles in high school. He had this super cool jacked-up truck we’d go to the sand dunes with. His buddies had dune buggies.

“My mom remarried, to an engineer at the Corvette Group at GM. So I’ve always been surrounded by really amazing cars, especially since my stepdad had access to the Corvette Group’s competitive fleet that they could compare themselves to — a Lamborghini Countach, a Lotus Esprit, Ferrari 308. Can you imagine being around those cars as a kid?”

It could scar a boy for life. Shepard, 37, still hasn’t gotten over it.

“I love car chase movies, and there have been some made over the past 30 years,” he says. “But not car chase comedies. Those disappeared with the Hal Needham movies. The ‘Cannonball’ movies, ‘Hooper.’ ‘Smokey and the Bandit’ is one of my favorites. I see that a couple of times a year — seen it hundreds of times.”

So Shepard, star of TV’s “Parenthood,” scene-stealer of “Baby Mama” and heart-stealer of “When in Rome” (where he met Bell), wanted to update the genre.

“I’m this weird mix — an actor, a comedian, a gun-owning liberal and a gear head. I thought, ‘I want to bring all those contradictions to a movie and see how it plays.’ ”

Shepard complains that he’s “too big” for the vintage Triumph TR5 he drives on “Parenthood.” He fell in love with the villain’s car in “Hit and Run,” a Cadillac CTS-V station wagon driven by a murderous and dreadlocked Bradley Cooper, playing the guy Shepard’s character went into witness protection to avoid.

“The fact that we, in the U.S., are making a 550 hp station wagon tells me we’re still winning. Only a great country could make that.”